1. Field of Invention
This invention is directed to detectors for interferometric distance measuring and surface profiling devices.
2. Description of Related Art
Laser interferometers are widely used to measure a distance to a sample surface and to measure a surface profile. Laser interferometers operate by splitting a source of coherent radiation into two beams, an object beam and a reference beam, using, for example, a beam splitter. The reference beam is directed to a reference mirror which is located at a fixed distance from the beam splitter. The object beam is directed to a sample surface which is located at some other distance from the beam splitter. The object beam is reflected from the sample surface, and is recombined with the reference beam at the beam splitter. The object beam and reference beam can be made to constructively or destructively interfere, depending on the relative phase of the object beam compared to the reference beam. A detector measures the intensity of the interference light, which is related to the phase difference between the object beam and the reference beam, which is, in turn, related to the difference between the object path length from the beam splitter to the sample surface and the reference path length from the beam splitter to the reference mirror.